I've been asked to "measure up" This ktm pot and piston. Apologies, don't have the piston right now. The young lady owner originally cooked the engine whilst racing, I think she was stuck in low gear or something, but pressed on and the result was she needed a new piston and barell.
Once fitted, gone through some heat cycles, she took it to work, and it locked up...
So I've measured it. the coated piston had around a thou and half clearance at bottom of skirt, 2 and a half at the top. The top surface of the piston was clean, no signs of overheating or det - the piston is coated and the bore has a nicasil or similar coating - low friction and also low expansion design apparently.
Anyway, this did not seize across the piston, it looks like the two ports controlled by some develish power valve thing got hot and melted, coating the piston which then turned its surface (in the area of the ports to mush. Can someone explain these ports to me please?
Then, another strange thing, there are two blank ports in the piston, which line up with nothing, go nowhere. If you turn the piston around, they line up with the ports that overheated - so I did ask, was the piston the wrong way round? No, apparently..
Pictures:-
Once fitted, gone through some heat cycles, she took it to work, and it locked up...
So I've measured it. the coated piston had around a thou and half clearance at bottom of skirt, 2 and a half at the top. The top surface of the piston was clean, no signs of overheating or det - the piston is coated and the bore has a nicasil or similar coating - low friction and also low expansion design apparently.
Anyway, this did not seize across the piston, it looks like the two ports controlled by some develish power valve thing got hot and melted, coating the piston which then turned its surface (in the area of the ports to mush. Can someone explain these ports to me please?
Then, another strange thing, there are two blank ports in the piston, which line up with nothing, go nowhere. If you turn the piston around, they line up with the ports that overheated - so I did ask, was the piston the wrong way round? No, apparently..
Pictures:-